docs: fix the docs to be CommonMark compliant

[Splaktar]

AngularJS is in LTS mode

We are no longer accepting changes that are not critical bug fixes into this project.
See https://blog.angular.io/stable-angularjs-and-long-term-support-7e077635ee9c for more detail.

I'm submitting a ...

• regression from 1.7.0
• security issue
• issue caused by a new browser version
• other

Current behavior:

• Described in PR chore(dgeni): update to latest dgeni and dgeni-packages #17141

Expected / new behavior:

• dgeni and dgeni-packages can be updated without breaking the markdown rendering of the docs

Minimal reproduction of the problem with instructions:

1. Update dgeni and dgeni-packages
2. Run the docs and see rendering issues with markdown.

AngularJS version: 1.8.2
Browser: all

Anything else:

The alternative to this labor intensive task is pinning marked to 0.3.6` as is done in PR #17141.

However, in #17141 (comment), Pete suggested that

Rather than pinning marked we should just fix the docs to be CommonMark compliant.